The present invention is directed to a sizing composition useful in producing sized glass fibers having improved stability to ultraviolet radiation.
More particularly, the present invention is directed to a sizing composition and sized glass fibers produced therewith that when used in reinforced polymers yield reinforced polymers with improved color stability when subjected to light.
Light is electromagnetic radiation in the wave length range including infrared, visible, ultraviolet, and X-rays. Only about five percent of the ultraviolet radiation emitted from the sun reaches the earth's surface and this five percent is usually radiation having wave lengths longer than 290 nanometers. The light produced from man-made sources such as fluorescent lights and the like can emit ultraviolet radiation (UV) that generally has wave lengths below 290 nanometers. Most organic substances including polymers or plastics are changed on long-term exposure to light including sun light and man-made light that contains ultraviolet radiation. Prolonged exposure of polymers to UV-containing light leads to photo oxidation and degradation of the polymer. This degradation is usually manifested in the discoloration of the polymer.
It is well known in the art to use additives for polymers that give some degree of UV stability to the polymer to retard the process of photo oxidation and degradation of the polymer upon exposure to light. There must be at least ten different classes of materials used as UV stabilizers for polymers. The principle classes of UV stabilizers are the benzophenones, benzotriazoles, the salicylates, metallic complexes, substituted acrylonitriles and certain colorants. Which class or particular stabilizer within a class that should be used with a particular type of polymer depends on the specific requirements relating to polymer compatibility, permanence, and the level of absorption needed for the particular polymer, because some polymers are more sensitive to UV radiation than others. For example, polyurethanes, which are produced by reacting polyols containing an active hydrogen with isocyanate, require stabilization against photo oxidation. It is known in the art in the case of polyurethanes that the hindered amine light stabilizers, like bis(2,2,6,6-tetramethyl-piperidinyl-4)sebacate and oxalic-anilide derivatives, in combination with benzotriazoles provide excellent UV stability. In addition to the use of UV stabilizers, it is also known to add functional groups to the backbone in order to retard the photo oxidation of the polymer caused by UV radiation.
Glass fibers used as reinforcement for polymers are formed by being drawn at a high rate of speed from molten cones of glass from tips of small orifices in a platinum device called a bushing. In order to protect the glass fibers from interfilament abrasion during formation and further processing and to make then compatible with the polymers they are to reinforce, the sizing composition is applied to the glass fibers during their formation. The sizing compositions conventionally contain lubricants, film formers, coupling agents, wetting agents, emulsifiers, and the like. Many of these components are polymeric materials that can degrade by photo oxidation when subjected to radiation. The degradation of the polymers in the sizing composition on glass fibers used to reinforce polymers may lead to the discoloration of the reinforced polymeric material. Such discoloration leads to an unaesthetic appearance of a reinforced polymeric material and lack of color uniformity over a period of time for reinforced polymeric material.